The concept that endothelial cells are only a passive lining of blood vessels has gradually changed within the past ten years with the discovery that lung alters the concentration of blood born vasoactive hormones, including the biogenic amines, as they transverse the pulmonary vasculature. Thus, lung can regulate, at least in part, the composition of vasoactive agents in blood reaching the systemic circulation. Though considerable information suggests that the endothelium of the pulmonary vasculature is the major site for these important metabolic reactions, direct evidence demonstrating this is lacking. Accordingly, the project proposed has the following objectives: 1) Attempt to characterize and compare amine disposition in cultured rabbit endothelial cells isolated from rabbit aorta. Included in this study would be the characterization of the enzymes principally responsible for amine inactivation and determination of the relative activities of these enzymes in these endothelial cells. 2) Isolate and establish endothelial cell lines in culture from rabbit pulmonary artery and vein by methods previously used to establish cultures of rabbit aorta endothelium. Characterize and compare the activities of these endothelial cells with that of rabbit aorta as described above. 3) Identify and compare alpha and beta receptor activity in the three endothelial cell lines maintained in culture. Preliminary studies have already demonstrated that cultured rabbit aorta endothelium readily transports and deaminates the biogenic amine, tyramine, and also contains both alpha and beta receptors.